Substances that are insoluble in both water and lipids are commonly assumed to be tasteless. However, rats given a choice of fluid containing dispersed starch and the same fluid without starch, consistently preferred fluids containing starch but did not respond to cellulose. Experiments are proposed to examine the mechanisms by which chemosensory systems may detect insoluble substances dispersed in water. The experiments will focus on rats' ability to detect starch and oil because of the potential to identify novel mechanisms and the relative ease with which starch and oil preference can be studied. The basic technique to be used is to offer rats dispersions of starch or oil in water, stabilized with xanthan gum, and observe preference behavior. In some experiments, conditioned aversion procedures will be used to determine whether different forms of starch taste similar to each other, and whether different triglyceride oils taste similar to each other. Other studies will examine the ability of rats to discriminate between different concentrations of starch and oil. This will provide information about how well chemosensory systems are adapted to meter energy intake. Other experiments will examine specific hypotheses about how insoluble substances may be detected. Experiments manipulating the viscosity of the test fluids will examine the role of tactile sensitivity. Experiments in which rats are offered starch samples differing in particle size will determine whether particle size influences the ability to detect starch. Experiments in which olfactory bulbs are surgically removed will determine whether olfaction contributes to chemosensitivity to starch or oil. The role of ionic and other physical effects of dispersed solids will be examined by adding sodium chloride and chilling starch dispersions offered to rats. These studies will provide basic information about chemoreception of insoluble substances.